I', 98 SODIUM CHLORATE substance) or with Leblanc soda, 50 c.c. ( = 5 grams) of solution are neu tralised exactly with N-nitric acid, the liquid boiled, 10 drops of 10% potas- sium chromate solution added, and N/io-silver nitrate run in from a burette until a red coloration appears, i c.c. N/io-silver nitrate = 0-005846 gram NaCl. (g) SODIUM SULPHATE. With Leblanc soda, 50 c.c. (~ 5 grams of substance) or with ammonia, soda, loo c.c. (~-~ 1:0 grams) of the solution are acidified with hydrochloric acid, heated to boiling, precipitated with barium chloride, filtered and the barium sulphate1 washed, dried, calcined and weighed: i gram of BaSO, ~; 0-6089 gram of NaaSO4. (//.) SILICA AND ALUMINA. 100 c.c. of the solution (~:ro grams of substance) are acidified with hydrochloric acid and evaporated on a water- bath, the residue being dried at 105" and taken up in hydrochloric acid ; the silica is separated and weighed, and the alumina estimated in the solution in the ordinary way. Commercial soda crystals .should contain a,t least 34% of N<u(X);i ; usually they contain 35% (theoretically 37-04;!% NaBC !(')., and <>.:-<>58% 1U>). Some- times a slight excess of water is present, but this should not exceed r% ; often slight efflorescence is shown. The ordinary impurity is sulphate (in Leblanc soda ; see later), but large proportions, such as to •-'.<)%, must; bo regarded as added artificially. The chloride content in Leblane soda, should not: exceed °'5%- The yellowish colour of certain soda crystals is usually derived from organic snbstane.es and not from iron. Calcined Lt'.hlan c> soda may contain small proportions of hydroxide, sulphide and sulphite, and is often contaminated with sulphate ; its strength may vary from 80 to 0.0%, but: is most, often H8 '95%. A HUIWH.M xtxfa, contains chloride, and sometimes small quantities of bicarbonate ; its strength is 95 -98%. The moisture of calcined soda is usually 0-5-1%, 3% being tolerated ; in moist air, calcined soda may absorb up to about; 10% of moisture, The insoluble substances in ordinary good soda should, not exceed 0-5%, of which about o-i % is insoluble in. hydrochloric acid and 0-02% ferric, oxide. The sulphate in ammonia soda, should not be more than 0-1%, if not added. In Leblanc soda of best quality 0-5 -'i % occurs, while in inferior qualities it reaches 8% or more. The chloride occurs to the extent of 0-5 -2'5% in ammonia soda or 0'25--o*5% in Leblanc soda, Pure or chemically pure- sodium Mtrhonaic. should answer all the qualitative tests, i-:t'4. SODIUM CHLORATE NaflCK, - 106-5 White, crystals or powder soluble in about i part of cold water. The commercial product does not reach the degree of purity of potassium chlorate, but usually contains small quantities of chlorides, lime and, some- times, iron. The various impurities and also the content of chlorate are investigated and determined as in potassium chlorate (<•/.«,) : i c.c. N/io- thiosulphatc —0-001775 gram NaC103.knowing that I c.c. of silver solution = 1-3 c.c. N/io-iodine.